1. Field of the Invention
This invention relates to a cell assembly and, in particular, to a cell assembly for a sensing element sensitive to the dissolved gas content of a flowing liquid stream.
2. Brief Statement of the Prior Art
There is disclosed, in U.S. Pat. No. 3,813,325, a continuous respirometer which has dissolved oxygen cells positioned at the inlet and outlet of a tubular flow passageway for determining the dissolved oxygen contents of a liquid stream entering and exiting the respirometer. The dissolved oxygen analyses are performed on a continuously flowing liquid stream with the tips of the cathodes projecting downwardly through bores in the top walls of tubular housings. It is disclosed that the probes fare in with the surfaces of the interior walls to avoid projections on which residue may build up.
Use of the forementioned respirometer has revealed that when the probes project into the stream even by a slight distance, air pockets developed on the upstream side of the projections and these air pockets are not exhausted during the purging of the apparatus, contributing to erroneous analyses for dissolved oxygen contents.
Although not illustrated in the aforementioned patent, commercial embodiments of the patented device have employed a temperature compensation circuit having a thermistor imposed in the path of flow through the electrode housing to compensate for changes in permeability with temperature of the plastic membranes which overlie the cathode surfaces and directly affect the readings of the oxygen cells. These thermistors were placed generally transverse in the housing, beneath the dissolved oxygen electrodes to be in contact with the fluid under investigation without imposing any significant pressure drop to fluid flow through the housing.